This invention refers to a vibration damper. Such vibration dampers are used in motor vehicles for damping the oscillations between the body work of the motor vehicle on the one hand and the wheels of the motor vehicles on the other hand.
More particularly the invention refers to the so-called twin tube vibration dampers or oscillation dampers which comprise a pressure tube and a casing tube surrounding the pressure tube.
In modern vibration dampers it is frequently necessary to provide on the radially outer side of the casing tube a flow control unit and more particularly a bypass valve unit. This flow control unit is used for controlling the flow of a damping fluid within the vibration damper. The flow control unit can be controlled by external signals, for example, electrical signals such as to alter the flow conditions of the damping fluid within the vibration damper. For example, it is possible to provide such a flow control unit in a bypass flow path bypassing a primary flow path which extends through a piston unit of the vibration damper. By opening or closing the flow control unit the bypass flow path can be either opened or closed. Opening of the bypass flow path has the effect that a softer damping station is obtained, whereas closing of the bypass flow path has the effect of obtaining a harder damping.
The flow control units and, more particularly, bypass valve units are frequently to be provided on a radially outer surface of the vibration damper and more particularly on the radially outer surface of a casing tube in case of a twin tube vibration damper.